This invention relates to a reinforced pressure vessel, and more particularly to a lined filament wound pressure vessel for containing gases under high pressure.
It is common practice to provide metal lined pressure vessels which are reinforced by an over-wrap of a cured, resin-impregnated, filament material, such as filament glass. Such cured resin impregnated filament pressure vessels are capable of containing high gas pressures at favorable weight to volume ratios. In spite of higher cost and weight, metal has been the material of choice for pressure vessel liners in view of the gas impermeability of the metal, thereby providing acceptably long high pressure storage times.
An example of a metal lined filament wound pressure vessel designed for storing gases under high pressure (up to 10,000 psi) is shown in Morse et al, U.S. Pat. No. 3,843,010 issued Oct. 22, 1974. In that patent, a pressure vessel with a thin metal liner is described as having a distinct advantage over non-metal lined pressure vessels from gas permeability and leakage rate standpoints. However, metal linings are relatively expensive and are prone to failure due to metal fatigue induced by repeated pressurizations and depressurizations.
Liners formed of injection molded, centrifugal cast or blown polyethylene, in the manufacture of an "allcomposite" cylinder or pressure vessel have also been attempted. Such liners have included blown, high density polyethylene with aluminum end bosses. However, the high gas permeability of polyethylene, including HDPE, has required such liners to have walls of substantial thicknesses for very high pressure gas retention, thereby losing the benefit of the lighter density and lower cost of this material compared to a metal liner. The relatively high gas permeability of HDPE has lead to investigations as to additives and surface treatments for further reducing permeation by gas through the liner.
Typical design pressures may exceed 3,000 psi for retaining compressed natural gas, as a fuel for automotive vehicle use. A leakage rate in excess of 0.25 cubic centimeters per hour per liter of capacity is considered to be excessive. Firemen's backpack air bottles represent a further example of the use of a composite wound high pressure vessel which must have a light weight and yet be very strong. They may be pressurized up 4,500 psi.